About how many deer were in the population?

Question

In a capture-recapture study, a biologist tagged and released 290 deer. A month later she captured 40 deer, 30 of which had tags.

Answer 1

There were a total of 70 deer in the capture.  30/70 = 3/7 of them were tagged.  It's reasonable to conclude that the original tagging tagged 3/7 of the total population.

 

Let x = the total population.  That leads to an equation:

 

290 = 3/7 x

290 / (3/7) = x

676.67 = x

 

Since there can't be a fraction of a deer, the estimate should be rounded to the nearest integer.  So there were approximately 677 deer in the population.